1. Field of the Invention
The present invention relates to an action for a piano which actuates in response to a depression on an associated key to swing a hammer which in turn strikes a string.
2. Description of the Prior Art
A known conventional action for a piano is disclosed, for example, in Laid-open Japanese Patent Application No. 6-83326. FIG. 1 illustrates main components of an action 51 in a key released state. The action 51 is adapted for an upright piano, and is disposed above the rear end of a key 50 (the left-hand side in FIG. 1 is assumed to be the rear side). The action 51 comprises a wippen 52 carried on the rear end of the key 50; a jack 53 pivotably arranged on the wippen 52; and a regulating button 56 disposed at a predetermined position above the wippen 52. The jack 53 is formed in L-shape with a regulating button contact protrusion 54 extending in the front-to-rear direction, and a hammer push-up rod 55 extending upward substantially at right angles with the rear end of the regulating button contact protrusion 54, and is pivotably supported by the wippen 52 at the corner of both members 54, 55. Also, in the key released state, the hammer push-up rod 55 is in engagement with a bat 61 of a hammer 60, and the regulating button contact protrusion 54 has a regulating button contact surface 54a opposing a regulating button 56 from below. The regulating button contact surface 54a is formed in a curved surface. The bat 61 is arranged such that a hammer shank 62 extends upward therefrom, and a hammer head (not shown) of the hammer 60 is mounted to the upper end of the hammer shank 62. Also, the bat 61 is provided with a bat spring 61a for urging the hammer 60 in the clockwise direction in FIG. 1.
As the key 50 is depressed in the upright piano as described above, the wippen 52 is pushed up by the rear end of the key 50 to pivotally move upward, causing the jack 53 to move up together with the wippen 52. In this way, the hammer 60 is pushed up by the jack 53 through the bat 61, and pivotally moves toward a vertically stretched string (not shown) in the rear against an urging force of the bat spring 61a. Then, as the regulating button contact protrusion 54 of the jack 53 comes into contact with a regulating button 56, the jack 53 is prevented from moving up. As the wippen 52 further pivotally moves, the regulating button contact protrusion 54 of the jack 53 pivotally moves with respect to the wippen 52 while sliding along the lower surface of the regulating button 56, with a counter-force from the regulating button 56 acting on the jack 53, resulting in the jack 53 coming off the hammer 60. Consequently, the weight of the hammer 60 is lost from a touch weight (a load applied on a finger tip) of the key 50, giving a let-off feeling to a player. After the jack 53 has come off the hammer 60, the hammer 60 strikes an associated string with the inertia.
Generally, for rich play representations, it is important to correctly pinpoint a timing at which the jack 53 comes off the hammer 60, i.e., a let-off timing to finely adjust the speed at which the hammer 60 strikes the string. For example, a weak sound such as pianissimo can be generated by once bringing the hammer 60 to the vicinity of the string and letting it swing from that position to reduce the string striking speed of the hammer 60. In other words, a weak sound can be generated by once depressing the key 50 to immediately before let-off at which the jack 53 comes off the hammer 60, and pushing down the key 50 from that state.
On the other hand, in the upright piano which employs the conventional action, the hammer shank 62 extends vertically as mentioned above, so that the center of gravity of the hammer 60 is positioned near the fulcrum of its swinging movements, resulting in small moment about the fulcrum of the swinging movements produced by the self weight of the hammer 60. For this reason, a let-off load, which is a touch weight immediately before the let-off, is relatively small, and the touch weight varies only by a small amount before and after the let-off, thus experiencing difficulties in pinpointing the timing of the let-off. As a result, the piano is degraded in its capabilities of expressions and playing performance due to difficulties in finely adjusting the string striking speed of the hammer 60.
Also, high sequentially touching capabilities are also required for rich playing expressions. In a grand piano, the hammer extends substantially horizontally, with its center of gravity positioned near a hammer head spaced largely from the fulcrum of pivotal movements at one end of the hammer in the horizontal direction. Thus, the hammer, after striking a string above, promptly swings by its own weight to return to a position at which it can be again pushed up by the jack, with the result that the grand piano provides high sequentially touching capabilities. On the other hand, in the aforementioned upright piano, since the hammer 60, after striking the string, is swung by an urging force of the bat spring 61a to return, a relatively long time is taken for the hammer 60 and jack 53 to return to a state in which the hammer 60 can be again pushed up, resulting in lower sequentially touching capabilities of the upright piano than the grand piano. For improving the sequentially touching capabilities of the upright piano, it is contemplated to enhance the spring force of the bat spring 61a to reduce a time for the hammer 60 to swing back to the position at which it can be again pushed up by the jack 53. In this strategy, however, the touch weight is increased by the enhanced spring force when the hammer 60 is pushed up by the jack 53, resulting in adverse affections exerted on the touch feeling.